A phase change memory device has the non-volatile characteristic of retaining its stored data even when power is removed form the memory device. A unit cell of a phase change memory device may include a phase change material used as an element of data storage. The phase change material may change into a crystallization state or an amorphous state according to a heat temperature and/or a heat supply time. Typically, a resistivity of a phase change material of a crystallization state is lower than that of an amorphous state. Using a resistivity change according to a state of a phase change material, a phase change memory cell may store logic data and discriminate it.
The phase change memory cell may include a selection element that is electrically connected to the phase change material used as the element of data storage. The selection element is required to select one among a plurality of the phase change memory cells. A MOS transistor is well known as the selection element. Typically, a MOS transistor includes source and drain regions spaced apart from each other, and a gate on a channel between the source and drain regions.
As the integration of semiconductor devices increases, phase change memory devices are also becoming highly integrated. Since a metal oxide semiconductor (MOS) transistor has a comparatively large area, it may be difficult to highly integrate a phase change memory cell including a MOS transistor.